source:clickhereGoing underground, expedition members enter Hang En, a cave tunneled out by the Rao Thuong River. Dwindling to a series of ponds during the dry months, the river can rise almost 300 feet (91 meters) during the flood season, covering the rocks where cavers stand.
Adventure to One of the World's Natural Wonders: Ha Long Bay, Vietnam [Eng-Esp]belug ·
